The present invention relates to a continuous positive airway pressure controller, and in particular, to such a controller for controlling the supply of oxygen to a respiratory circuit of a subject.
Such controllers supply oxygen or oxygen enriched air to a subject. Typically, the controller delivers the oxygen or oxygen enriched air to a respiratory circuit which feeds the oxygen or oxygen enriched air to the subject. In general, such controllers comprise a venturi mixer for mixing ambient air with oxygen for delivery to the subject. The oxygen, typically is derived from a pressurised source, such as a pressurised container, typically referred to as an oxygen bottle. In general, a primary supply of oxygen is delivered to the venturi mixer through a main jet from an inlet port of the controller. Air to be mixed with the oxygen is drawn into the venturi mixer by the primary oxygen issuing from the main jet, and an oxygen/air mix is delivered from an outlet port to the subject""s respiratory circuit. A secondary supply of oxygen is delivered from the inlet port of the controller to the venturi mixer for enriching the air which is being drawn into the venturi mixer by the primary oxygen issuing from the main jet. In general, a flow regulator valve is provided for regulating the secondary oxygen supply to the venturi mixer for in turn regulating the proportion of oxygen in the oxygen/air mix from the venturi mixer. Typically, the proportion of oxygen in the oxygen/air mix may be varied within the range of 30% oxygen to 100% oxygen.
However, such controllers suffer from a number of disadvantages. Firstly, it is not possible to adjust the proportion of oxygen in the oxygen/air mix without altering the flow rate of the oxygen/air mix. To adjust the proportion of oxygen in the oxygen air mix, the flow regulator valve is adjusted for adjusting the secondary oxygen supply to the venturi mixer. This, thus, causes a change in pressure of the primary oxygen supply to the main jet, thereby altering the flow rate of the primary oxygen through the main jet, which in turn reduces the flow rate of the oxygen/air mix from the outlet port. This leads to significant problems, in that if it is desired to adjust the oxygen proportion of the oxygen/air mix a considerable number of adjustments are required subsequently in order to re-establish the desired flow rate with the desired oxygen proportion after adjustment of the oxygen/air mix ratio. A further disadvantage of such known controllers is that it is not possible to vary the flow rate of the oxygen/air mix without altering the oxygen/air mix ratio. Accordingly further adjustments are required to the flow rate of the secondary oxygen after a desired flow rate of the oxygen/air mix has been established. In many cases a series of alternate adjustments to the flow rate of the oxygen/air mix and the secondary oxygen are required before the desired flow rate and oxygen proportion of oxygen/air mix can be established.
There is therefore a need for a controller suitable for operating with a continuous positive airway pressure which address at least some of these problems.
The present invention is directed towards providing such a continuous positive airway pressure controller.
According to the invention, there is provided a continuous positive airway pressure controller for supplying a regulated oxygen/air mix to a respiratory circuit, the controller comprising a main oxygen inlet port for connecting to an oxygen supply source, a venturi mixing means located in a venturi accommodating chamber for blending oxygen and air to form the oxygen/air mix, a main jet means communicating with the main oxygen inlet port for delivering a primary oxygen supply through the venturi mixing means for drawing air from the venturi accommodating chamber into the venturi mixing means for blending air with the primary oxygen to form the oxygen/air mix, an air inlet to the venturi accommodation chamber for communicating the venturi accommodating chamber with ambient air, a secondary oxygen communicating means communicates the venturi accommodating chamber with the main oxygen inlet port for delivering a secondary oxygen supply into the venturi accommodating chamber for enriching the oxygen/air mix, and a main outlet port from the venturi mixing means for delivering the oxygen/air mix, wherein a secondary flow control means is provided for regulating the flow of oxygen through the secondary oxygen communicating means for varying the ratio of the oxygen to air of the oxygen/air mix delivered from the main outlet port, and a pressure regulating means is provided for maintaining the pressure of the oxygen being delivered to the main jet means and to the secondary flow control means substantially similar, and for varying the flow rate of the oxygen/air mix delivered from the main outlet port independently of the ratio of the oxygen to air of the oxygen/air mix.
In one embodiment of the invention a primary flow control means is provided for regulating the flow rate of the primary oxygen to the main jet means for accommodating different back pressures at the main outlet port caused by different operating pressures in respiratory circuits to which the main outlet port may be connected for delivering the oxygen/air mix. Preferably, the primary flow control means is fed from the pressure regulating means. Ideally, the primary flow control means is operable in a plurality of discrete configurations, which correspond with predetermined back pressures at the main outlet port caused by the different operating pressures in respiratory circuits to which the main outlet port may be connected.
In one embodiment of the invention the primary flow control means comprises a primary flow control valve.
In another embodiment of the invention a primary scale means is provided associated with the primary flow control means for facilitating selection of a desired configuration in which the primary flow control means is to operate.
Preferably, the secondary flow control valve is fed from the pressure regulating means.
In another embodiment of the invention a secondary scale means is provided associated with the secondary flow control means for facilitating selection of a desired operating configuration of the secondary flow control means for providing a desired ratio of oxygen to air of the oxygen/air mix.
In one embodiment of the invention the secondary flow control means comprises a secondary flow control valve.
In a further embodiment of the invention the pressure regulating means delivers a pressure regulated supply of oxygen to a main gallery from which the primary oxygen supply and the secondary oxygen supply are derived, the main gallery being sized for maintaining the oxygen pressure at the pressure set by the pressure regulating means throughout the main gallery.
In one embodiment of the invention the venturi mixing means comprises a venturi tube having an upstream inlet, the main jet means defining with the upstream inlet an annular opening which communicates the venturi tube with the venturi accommodating chamber for receiving air and the secondary oxygen supply into the venturi tube.
In another embodiment of the invention a back pressure monitoring means is provided for monitoring back pressure at the main outlet port.
Preferably, a first control means is provided for reading back pressure monitored by the back pressure monitoring means, and for controlling the primary flow control means in response to the back pressure monitored by the back pressure monitoring means for in turn accommodating different back pressures at the main outlet port caused by different operating pressures in respiratory circuits to which the main outlet port may be connected.
Advantageously, a second control means is provided for controlling the flow rate of the oxygen/air mix from the main outlet port for compensating for an excessive negative back pressure differential during an inspiration period of a breathing cycle of a subject, and for compensating for an excessive positive back pressure differential during an exhalation period of a breathing cycle, the second control means comprising a means for reading back pressure monitored by the back pressure monitoring means, and being responsive to the second control means determining that the negative and/or positive back pressure differentials during inspiration and/or exhalation are greater than respective predetermined reference negative and positive pressure differential values for controlling the pressure regulating means for varying the pressure of the oxygen for in turn varying the flow rate of the primary oxygen through the jet means for in turn varying the flow rate of the oxygen/air mix.
In one embodiment of the invention the second control means reads the back pressure monitored by the back pressure monitoring means at the main outlet port over a plurality of breathing cycles and determines the respective negative and positive average pressure differentials over the plurality of breathing cycles. Preferably, the second control means determines the respective average negative and positive pressure differentials over a predetermined number of breathing cycles. Advantageously, the second control means determines the respective average negative and positive pressure differentials over at least five breathing cycles. Ideally, the second control means averages the respective negative and positive back pressure differentials during the respective inspiration and exhalation periods over the plurality of breathing cycles.
In one embodiment of the invention the second control means controls the pressure regulating means for increasing the oxygen pressure for in turn increasing the flow rate of the oxygen/air mix from the main outlet port by a first predetermined increment in response to the average negative back pressure differential during the inspiration periods of the breathing cycles being greater than the reference negative pressure differential value.
In one embodiment of the invention each first predetermined increment of flow rate is at least 1 liter per minute. Preferably, each first predetermined increment of flow rate is at least 3 liters per minute. Ideally, each first predetermined increment of flow rate is approximately 5 liters per minute.
In another embodiment of the invention the second control means operates the pressure regulating means for decreasing the flow rate of the oxygen/air mix by a first predetermined decrement on the average negative back pressure differential during the inspiration period of the breathing cycles being less than the reference negative pressure differential value. Preferably, the value of each first predetermined decrement is less than the value of the first predetermined increment. Advantageously, the value of each first predetermined decrement is less than 3 liters per minute. Preferably, the value of each first predetermined decrement is less than 2 liters per minute. Ideally, the value of each first predetermined decrement is approximately 1 liter per minute.
In another embodiment of the invention the second control means operates the pressure regulating means for increasing the flow rate of the oxygen/air mix by a second predetermined increment on the average negative back pressure differential during the inspiration periods of the breathing cycles being greater than the reference negative pressure differential value after the flow rate of the oxygen/air mix has been reduced as a result of controlling the pressure regulating means for reducing the flow rate by one or more first predetermined decrements. Preferably, the value of each second predetermined increment is less than 3 liters per minute. Advantageously, the value of each second predetermined increment is less than 2 liters per minute. Ideally, the value of each second predetermined increment is approximately 1 liter per minute.
In a further embodiment of the invention the second control means controls the pressure regulating means for decreasing the flow rate of the oxygen/air mix from the main outlet port by a second predetermined decrement in response to the average positive back pressure differential during the exhalation period of the breathing cycles being greater than the reference positive pressure differential value. Preferably, each second predetermined decrement of flow rate is at least 1 liter per minute. Advantageously, each second predetermined decrement of flow rate is at least 3 liters per minute. Ideally, each second predetermined decrement of flow rate is approximately 5 liters per minute.
In a still further embodiment of the invention the second control means operates the pressure regulating means for increasing the flow rate of the oxygen/air mix by a third predetermined increment on the average positive back pressure differential during the exhalation periods of the breathing cycles being less than the reference positive pressure differential value. Preferably, the value of each third predetermined increment is less than the value of the second predetermined decrement. Advantageously, the value of each third predetermined increment is less than 3 liters per minute. Ideally, the value of each third predetermined incremented is less than 2 liters per minute, and more preferably, the value of each third predetermined increment is approximately 1 liter per minute.
In a further embodiment of the invention the second control means operates the pressure regulating means for decreasing the flow rate of the oxygen/air mix by a third predetermined decrement on the average positive back pressure differential during the exhalation periods of the breathing cycles being greater than the reference positive pressure differential value after the flow rate of the oxygen/air mix has been increased as a result of controlling the pressure regulating means for increasing the flow rate by one or more or the third predetermined increments. Preferably, the value of each third predetermined decrement is less than 3 liters per minute. Advantageously, the value of each third predetermined decrement is less than 2 liters per minute. Ideally, the value of each third predetermined decrement is approximately 1 liter per minute.
In a still further embodiment of the invention a supply pressure monitoring means is provided for monitoring the oxygen supply pressure from the oxygen supply source, and a switch means is provided responsive to the supply pressure monitoring means for isolating the first and second control means from a power supply means the oxygen supply pressure falling below a predetermined level. Preferably, the power supply means is a battery operated power supply means.
The advantages of the invention are many. The main advantage and most important advantage is that the ratio of oxygen to air of the oxygen/air mix from the main outlet port may be adjusted independently of the flow rate of the oxygen/air mix from the main outlet port, and vice versa. This important advantage is achieved by virtue of the fact that the flow rate of the oxygen/air mix is set and varied by the pressure regulating means, and accordingly, once the oxygen pressure in the controller has been set to give the desired flow rate of oxygen/air mix the oxygen pressure in the controller remains constant for a given flow rate of oxygen/air mix irrespective of alteration to the ratio of oxygen to air of the oxygen/air mix. Additionally, once the ratio of oxygen to air of the oxygen/air mix has been set by the secondary flow control means the flow rate of the oxygen/air mix can be varied by the pressure regulating means without affecting the ratio of oxygen to air of the oxygen/air mix due to the fact that the pressure regulating means maintains the oxygen pressure at the main jet means and the secondary flow control means similar after the oxygen pressure has been altered by the pressure regulating means, thereby leaving the ratio of oxygen to air in the oxygen/air mix unaltered.
By providing a monitoring means for monitoring back pressure at the main outlet port, and a first control means for controlling the primary control means in response to the back pressure monitored by the monitoring means the primary flow control means may be set to provide a flow rate of primary oxygen to the main jet means for in turn providing the oxygen/air mix at a flow rate to match the monitored back pressure. This aspect of the invention provides a particularly important advantage where it is likely that the pressure controller may be used with respiratory circuits which are to operate at respective different back pressures. It facilitates matching the flow rate of the oxygen/air mix with the back pressure at which the respiratory circuit is operating. It will be appreciated that the flow rate of the oxygen/air mix from the main outlet port would vary for different back pressures, and as the flow rate dropped as the back pressure increased the venturi mixing means would become less efficient, thereby possibly altering the ratio of the oxygen/air mix. By being able to compensate for different back pressures resulting from different respiratory circuits allows efficient operation of the controller with a wide range of respiratory circuits.
A further advantage of the invention is derived when the second control means is provided for controlling the flow rate of the oxygen/air mix from the main outlet port for compensating for an excessive pressure differential during inspiration and/or exhalation periods of a breathing cycle, since the provision of the second control means facilitates reduction of the back pressure differential to an optimised level during inspiration and exhalation periods.